Startup Claims Cellular Breakthrough

The Artemis approach turns Shannon's Law on its head, Perlman claims. Rather than manage spectrum in coherent channels of non-interfering signals, Artemis embraces interference using a form of distributed antenna technology that Perlman published a paper on in July 2011.

The startup relies on software running in data centers to create virtual eNodeB base station services that are shared across multiple antennas in a network. The x86 Linux servers also generate virtual INQ waveforms, creating a virtual radio signal in software, said Perlman. In this way, the approach is roughly similar to a so-called cloud radio access network now in pilot testing at China Mobile and a handful of partners.

Artemis replaces a physical base station with a simpler "radio head" that converts and transmits the virtual signals as waveforms. The pCell radio head is based on a Texas Instruments TCI6630K2L SoC with an analog front end and power amp. Perlman has lined up a Silicon Valley partner to make the radio heads. He also is willing to license the technology to telecom OEMs.

An Artemis radio head works in conjunction with datacenter servers to virtualize an eNodeB's functions on a cellular network.

Using the approach, radio heads on an estimated 350 rooftops with just four fibre backhaul links could cover all San Francisco. They are linked on a mesh networking using mainly line-of-sight millimeter wave connections.

So far, the Artemis technology is only geared for use with data on LTE networks. Carriers could wade into the new technology in steps, Perlman said, deploying it first in congested areas, gradually expanding out with the deployment of 4G.

Perlman said Sprint provided Artemis spectrum for experimental use. He implied the startup has had discussions with several other carriers, including Clearwire and Japan's Softbank. "We are trying to figure out which companies we will partner with, and all of them want some degree of exclusivity… [but] we've already said no time and time again on exclusivity," Perlman said. "We'd prefer not to close off the world and limit access to this technology," he added.

Although it has a staff of just eight full time engineers, Perlman said the startup is ready to support a small-scale deployment late this year and a full-scale launch in early 2015. The technology currently supports the 90 millisecond latency of LTE, but could be upgraded to support latencies as low as 5 ms.

Perlman planned a live demo of an Artemis pCell at Columbia University on February 19, the same place he gave his first talk about his distributed antenna technology.

Rick, what the paper describes is otherwise known as MIMO. Each AP transmits a signal on the same frequency channel. As long as the receivers can decorrelate the propagation paths from the different APs, they can reconstruct the desired signal.

In traditional MIMO, each transmitter sends multiple beams in different directions, and each receiver would combine the bit streams from all of the propagation paths. In this DIDO, it looks like each receiver is only interested in one of the propagation paths, rather than aggregating the signals from all of the paths. The net effect is the same, though.

These are clever techniques that APPEAR to violate Shannon's limit, but in fact they don't. They depend on decorrelated propagation paths, much as you would have if you used multiple separate cables in parallel. If the signals paths become more correlated, you will lose that spectral efficiency. For example, bring the APs physically very close together compared with the distance to the receivers. That sort of thing makes it difficult to decorrelate the different propagation paths.